The present invention relates to a method of and apparatus for controlling the flow rate of air intake of an internal combustion engine, particularly during idling.
There is known a method of controlling the air intake of an internal combustion engine when a throttle valve disposed in an intake passage is at the fully closed position. According to this conventional method, the flow rate of intake air, when the throttle valve is fully closed, is controlled by means of a control valve disposed in an air bypass passage which interconnects the intake passage at a position located upstream of the throttle valve with the intake passage at a position located downstream of the throttle valve. Such an air intake control method is usually employed for controlling the idling rotational speed of the engine. The idling rotational speed can be controlled by a closed loop if the bypass control valve is adjusted to control the flow rate of the air sucked into the engine through the bypass passage so that the detected actual rotational speed of the engine becomes equal to the desired idling rotational speed.
If a load is placed on the engine during idling, (e.g., the air) conditioner driven by the engine is operated or the shift position of the automatic transmission is changed from the neutral range or the parking range (these ranges are hereinafter referred to as the N range) to another range, such as the drive range (hereinafter referred to as D range) during the idling condition) a drive signal for actuating the bypass control valve is increased (or sometimes decreased) by a predetermined value independent of the above-mentioned closed loop control operation to increase (or decrease) the flow rate of air passing through the air bypass passage by a predetermined amount. If the exerted load is removed during idling (,e.g. if the air conditioner is switched off or if the shift position of the automatic transmission is changed from the D range to the N range, the drive signal is decreased by a predetermined value causing the bypass air-flow rate to be decreased by a predetermined amount. Thus, the response of the engine during idling can be improved by additionally increasing or decreasing the bypass air-flow rate by an amount which corresponds to the applied or removed load.
However, according to the conventional technique, since the additionally increased or decreased amount of the bypass air-flow rate responsive to the application or removal of the fixed load is always maintained at a predetermined fixed value, the following problems occur. For example, if a desired idling rotational speed, such as when the air conditioner is operating (when the air conditioner actuating switch is in an on-condition) is determined depending upon the atmospheric temperature (the temperature of the intake air or the temperature of air surrounding the engine), if the bypass air-flow rate is additionally increased or decreased by a common fixed amount in response to the on-off operation of the air conditioner actuating switch, the idling rotational speed of the engine may overshoot the desired value at the on-off operation of the air conditioner actuating switch causing torque-shocks to occur. Furthermore, due to the overshooting, the idling rotational speed is greatly delayed from converging to a desired speed, and thus the driving feeling of the engine is deteriorated. The same inconvenience during the on-off operation of the air conditioner actuating switch occurs when the automatic transmission is shifted from the D range to the N range and vice versa.